Manufacturing method for a wood composite layered material

ABSTRACT

A multi-layered composite building material is provided which allows effective utilization of forest resources by using so-called low quality materials such as small-diameter wood, old wood, pieces of wood produced as byproducts of lumbering, and/or bamboo. The material can meet various requirements and properties, and can be produced at a low cost. In a structural layer, an adhesive agent is applied to a plurality of finely split pieces which are formed by finely splitting a raw material such as wood or bamboo. The finely split pieces are arranging in parallel to a fiber direction. A shock/vibration-absorbing layer is formed by applying an adhesive agent to small pieces of wood and bamboo and the like. Structural layers and shock/vibration-absorbing layers are alternately arranged to provide a multi-layered structure. The structure is press-molded to a predetermined thickness and optionally heated such that the layers are adhered together to produce the composite multi-layered material. The shock/vibration-absorbing layer may be mixed with resin formed, for example, as a pellet shape, to provide a mixed vibration-absorbing material with improved properties.

This application is a divisional of commonly assigned, copending U.S.patent application Ser. No. 08/753,897 filed Dec. 2, 1996.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus and method for providing amulti-layered lumber product which effectively utilizes a relatively lowquality material such as small-diameter wood, old wood, pieces of woodwhich are byproducts of lumbering, and bamboo. Heretofore, suchrelatively low qualities materials have not been effectively utilized.

For a long time now, materials belonging to a wood group have beenformed into lumbered products by cutting raw wood. Conventionally,lumbered products are formed into a plate material for use in floors,walls, roofs and the like. A desirable minimum size of such a plate foruse in houses and other buildings or structural objects may be, forexample, 1800 mm in length by 900 mm in breadth. However, since a platematerial having such a size can be made only by a raw wood materialhaving a diameter of more than 900 mm, the yield from the raw wood isvery low. Thus, presently, production of such plates from raw wood isprohibitively expensive due to lack of a sufficient quantity of rawwood, production costs, and the like.

Materials which have been used heretofore to supplement lumberedproducts include plywood, particle board, and fiberboard. Plywood is amulti-layered material with a number of adhered veneer which does notrequire a cutting process by a saw as with the usual lumbering process,and can provide a yield from the raw wood of 60-70%. However, since theveneer is made by using a rotating cutter to peel thin layers from theraw wood, the material which can be used is limited to raw wood having alarge diameter.

With particle board or fiberboard, which comprise layers of pressed andmolded wood particles obtained by cutting the wood, since the composingelement is small, the yield from raw wood can be as high as 80-90%.Additionally, small-diameter wood, waste material from plant or houseconstruction, and broken wood can be used as a raw material, butstrength and stiffness are decreased relative to plywood. Generally,particle board includes any of various composition boards which areformed from small particles of wood, such as flakes or shavings, whichare bonded together with a resin. Fiberboard is a building material madeof wood or other plant fibers which are compressed and cemented intorigid sheets.

As it is known, since wood materials and bamboo have many advantages,including high-quality and beauty, and ease of obtaining, processing andreproducing, they have been widely used for many years. However, inconcomitance with an increasing world population and human life spans,the quantity of wood material used has been remarkably increased, andthe requirement for additional wood materials for various uses hasincreased.

To this end, as described above, new wood group materials such asplywood, particle board, fiberboard and the like have been developed, inparticular, for use in constructing plate-like boards for flooring,siding, roofing and other applications.

However, with plywood, particle board, and fiberboard, effectiveutilization of forest resources is still limited. In particular, plywoodmust be fashioned from raw wood having a large diameter, and, eventhough particle board and fiberboard can utilize 80-90% of raw wood,they do not possess the necessary properties for a structural platematerial which is used in houses, other buildings, and structuralobjects, such as furniture and the like.

Nowadays, as forest resources are increasingly depleted and resultingenvironment conditions are deteriorated due to the use of wood as amaterial for furniture, building materials, and structural materials,there is an urgent need for the development of an improved technique formaking plate materials which have the required properties for use inhouses, other building and structural objects, and wherein theproduction of waste parts is minimized, regardless of how large or smallthe standing wood or raw wood is.

Furthermore, since the above-described conventional plate materials donot possess good shock- and vibration-absorbing properties, there hasbeen a problem in providing floor materials for use in stairways ofmultiple floor buildings, or in flooring for areas with high pedestriantraffic, or in other floor applications.

Accordingly, it would be desirable to provide a building material whichefficiently utilizes raw wood materials while also providing goodproperties, including high strength, and good shock and vibrationabsorption. The present invention provides a method and apparatus havingthe above and other advantages.

SUMMARY OF THE INVENTION

In accordance with the present invention, a novel wood group buildingmaterial which solves the above-described conventional problems ispresented. The composite piled (e.g., multi-layered) material inaccordance with the present invention is made by combining a structurallayer and a shock/vibration-absorbing layer. The structural layer uses aplurality of finely split pieces formed by splitting a fibrous rawmaterial such as wood or bamboo in the fiber direction. Theshock/vibration-absorbing layer uses small pieces of raw material suchas wood and bamboo which are not necessarily aligned along a fiberdirection.

Further, although a small-diameter log of Japanese cedar was used as araw wood in example embodiments herein, it is possible to use a lowquality wood of bamboo, willow and the like, broken branches, pieces ofwood which are byproducts of the lumbering of raw wood, and waste woodfrom demolished buildings or the like. Moreover, the above low qualitywoods can be used independently or mixed together.

A composite multi-layered building material of the present inventioncomprises at least one structural layer and at least one shock/vibrationabsorbing layer. The structural layer comprises a number of elongatedpieces or strands of a fibrous raw material which are arrangedsubstantially parallel to one another. The pieces are adhered to oneanother by an adhesive agent. Moreover, one or more of the structurallayers and the shock/vibration-absorbing layers are arranged in aplurality of layers in an alternating manner to form a multi-layeredstructure. The multi-layered structure is pressed to a predeterminedthickness thereby causing the layers to adhere to one another to providethe multi-layered material as a unitary, substantially rigid body whichis suitable for building. The multi-layered structure may be heated to atemperature of approximately 180° C. while being pressed to cause thelayers to adhere to one another.

Additionally, the shock/vibration-absorbing layer may comprise at leastone of particle board and fiberboard. The shock/vibration-absorbinglayer may also comprise a denatured petroleum resin including at leastone of polyvinyl chloride, polyurethane, polyvinyl acetate, acrylicresin, natural gum, butadiene-styrene rubber, nitrile rubber, andchloroprene-copolymer, or a mixture of any of these resins. Moreover,the resin may be formed to a pellet shape which is a load-bearingelement.

The multi-layered material may comprise the structural layers (S1) andthe vibration/shock-absorbing layers (P) in the sequence S1:P:S1, oralternatively, P:S1:P.

Moreover, the multi-layered material may comprise at least first andsecond structural layers; where the plurality of elongated pieces of thefirst structural layer are arranged substantially orthogonal to theplurality of elongated pieces of the second structural layer. In oneembodiment, the weight of the structural layers is equal to the weightof the shock/vibration-absorbing layers.

Corresponding methods are also provided.

As explained above, in accordance with the present invention,small-diameter and low quality woods such as broken branches, pieces ofwood which are byproducts of the lumbering process, waste wood fromdemolished buildings and the like which have previously not beenutilized can now be utilized without waste. Accordingly, the yield ofthe raw material is very high, and an effective utilization rate offorest resources can be greatly increased.

Furthermore, by changing the number of layers of the arrangement ofstructural layers and shock/vibration-absorbing layers, a product havinga tailored strength, stiffness, hardness, softness, and/or otherqualities can be easily provided which has not been available inconventional wood materials. Thus, a novel wood group material havingproperties which conform to the intended application can be easilyprovided.

Further, a wood material having excellent shock and vibration-absorbingproperties which have not been available in conventional wood materialscan be realized. Accordingly, by using the composite multi-layeredmaterial of the present invention in a house or other building, floor,structural object, roof, wall, or the like, improved properties whichcould not been obtained in conventional wood materials can be realizedat a very low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and (b) are perspective views illustrating the manufacturingprocess of finely split pieces in accordance with the present invention.

FIG. 2(a) is a perspective view illustrating a molding frame forobtaining a composite multi-layered material including two structurallayers and one shock/vibration-absorbing layer in accordance with thepresent invention.

FIG. 2(b) is a cross-sectional view illustrating a compositemulti-layered material including two structural layers and oneshock/vibration-absorbing layer in accordance with the presentinvention.

FIG. 2(c) is a cross-sectional view illustrating the heat-pressing of acomposite multi-layered material including two structural layers and oneshock/vibration-absorbing layer in accordance with the presentinvention.

FIG. 3 is a perspective, partial cutaway view of a first embodiment of acomposite multi-layered material having three layers in accordance withthe present invention.

FIG. 4 is a perspective, partial cutaway view of a second embodiment ofa composite multi-layered material having three layers in accordancewith the present invention.

FIG. 5 is a perspective, partial cutaway view of a third embodiment of acomposite multi-layered material having seven layers in accordance withthe present invention.

FIG. 6 is a perspective, partial cutaway view of a fourth embodiment ofa composite multi-layered material having seven layers in accordancewith the present invention.

FIG. 7 is a graph comparing the bending strength of each compositemulti-layered plate shown in FIGS. 3-6.

FIG. 8 is a graph comparing the bending Young's coefficient of eachcomposite multi-layered plate shown in FIGS. 3-6.

FIG. 9 is a graph comparing the peeling-off strength of each compositemulti-layered plate shown in FIGS. 3-6.

FIG. 10 is a graph comparing a surface roughness of each compositemulti-layered plate shown in FIGS. 3-6.

FIG. 11 is a graph comparing a loss coefficient of the compositemulti-layered plate shown in FIG. 3 with and without a mixedvibration-absorbing layer.

FIG. 12 is a graph comparing a loss coefficient of the compositemulti-layered plate shown in FIG. 4 with and without a mixedvibration-absorbing layer.

FIG. 13 is a graph comparing a loss coefficient of the compositemulti-layered plate shown in FIG. 5 with and without a mixedvibration-absorbing layer.

FIG. 14 is a graph comparing a loss coefficient of the compositemulti-layered plate shown in FIG. 5 with and without a mixedvibration-absorbing layer.

FIGS. 15(a) and (b) are diagrammatic cross sectional views whichillustrate an operational concept of the shock/vibration-absorbing layerin accordance with the present invention.

FIG. 16 is a graph illustrating a change of Young's coefficient when thetotal weight of the structural layer and shock/vibration-absorbinglayers are equal, and the arrangement of the layers is varied.

FIG. 17 is a graph illustrating a relation of Young's coefficient andthe changes of weight ratio of the structural layer and theshock/vibration-absorbing layer, where the arrangement of the layers isconstant.

DETAILED DESCRIPTION OF THE INVENTION

A method and apparatus are presented for a composite multi-layeredbuilding material having good properties which efficiently utilizes woodresources.

FIGS. 1(a) and (b) are perspective views illustrating the manufacturingprocess of finely split pieces in accordance with the present invention.Firstly, as shown in FIG. 1(a), for a finely split piece to be used in astructural layer, a predetermined size material 2 is obtained by cuttingraw wood 1, for example, a small-diameter log such as a Japanese cedarwith a length of 400 mm. The raw wood 1 may be cut a plurality of timesto provide the plate material 2, which may have a thickness of 25 mm.Note that all dimension given herein are examples only, and theinvention may be adapted to various sizes and shapes of raw wood andfinished product.

As shown in FIG. 1(b), the predetermined size material 2 is split againin the fiber direction (e.g., along the grain) to produce a splitmaterial 3 with a 10 mm thickness. The split material 3 is furtherfinely split along the fiber direction to form finely split pieceshaving a cross section, for example, of 4×10 mm. For the splitting ofthe raw wood 1, a splitting device according to Japanese patentapplication Hei-5-352271 may be used. Also of interest are Japaneselaid-open patent Hei-7-195313, U.S. Pat. No. 5,441,787, and U.S. Pat.No. 5,505,238, all of which are assigned to the assignee herein.

FIG. 2(a) is a perspective view illustrating a molding frame forobtaining a composite multi-layered material including two structurallayers and one shock/vibration-absorbing layer in accordance with thepresent invention. Small pieces 6 of a wood group material are used toprovide a shock/vibration-absorbing layer. The small pieces 6 are madeby the same process which is used for manufacturing of conventionalparticle board or the like. The finely split pieces 4 obtained from theabove-described process and small pieces 6 of the wood group materialare separately dried (i.e., before layering), and a phenol resinadhesive agent is sprayed separately within a rotary drum. The adhesiveagent comprises approximately 10% of the weight of each of the finelysplit pieces 4 and small pieces 6. Successively, a plurality of finelysplit pieces receive the adhesive agent and are arranged within amolding frame 5, which may be 400×400 mm. The finely split pieces 4 arearranged in a lengthwise (e.g., fiber) direction to form a structurallayer S1, and small pieces 6 are multi-layered on it so as to form ashock/vibration-absorbing layer P.

FIG. 2(b) is a cross-sectional view illustrating a compositemulti-layered material including two structural layers and oneshock/vibration-absorbing layer in accordance with the presentinvention. The arranging of a number of structural andshock/vibration-absorbing layers may be repeated in turn, for example,to form a multi-layered body 7 which has alternating structural layer S1and a shock/vibration-absorbing layer P.

Furthermore, although a lowermost layer is formed as a structural layer1 at above, it is possible even when this is changed by theshock/vibration-absorbing layer P, and a uppermost layer is also formedby the shock/vibration-absorbing layer P.

And, although the weight of the finely split pieces 4 and the smallpieces 6 of each aforementioned layer may be approximately equal, thisis not required. That is, for each layer, the weights of the finelysplit pieces 4 and the small pieces 6 used for each layer need not beequal. Additionally, an overall desired ratio of weight to number oflayers may be constant or varied.

Further, it is possible to provide an orthogonal arrangement of thefinely split pieces 4 of the structural layers S1, or of the smallpieces 6 of the shock/vibration-absorbing layer P, where each of thefinely split pieces is considered to have some defined lengthwisedimension. For example, the finely split pieces 4 of the bottomstructural layer may be substantially orthogonal to the finely splitpieces 4 of the top structural layer. Within a single layer, the finelysplit pieces are substantially parallel. Alternatively, the finely splitpieces 4 of the bottom structural layer may be substantially parallel tothe finely split pieces 4 of the top structural layer. Moreover, theseconfigurations can be extended to any number of layers.

And, when a vibration-absorbing material is spread and mixed withoutadding the small pieces 6 to the shock/vibration-absorbing layer P, acapacity of the shock/vibration-absorbing layer P can be increased. Forexample, a vibration-absorbing material selecting from the group ofpolyvinyl chloride, polyurethane, polyvinyl acetate, acrylic resin,natural gum, butadiene-styrene rubber, nitrile rubber,chloroprenecopolymer, or other denatured petroleum resin may be used.And, a mixture or combination of the aforementioned substances may beused. Furthermore, although the vibration-absorbing material is shownherein as comprising pellet-shaped small pieces, it is possible to useother shapes, such as a particle-shape, needle-shape, wafer-shape,strand-shape, or sheet-shape.

FIG. 2(c) is a cross-sectional view illustrating the heat-pressing of acomposite multi-layered material including two structural layers and oneshock/vibration-absorbing layer in accordance with the presentinvention. The multi-layered body 7 obtained with the aforementionedprocess is pressed and tightened at a press which includes a spacer Sand a hot press H. The press exerts a pressure of, for example, 30 to 45kilograms force per square centimeter (kgf/cm²), at a temperature of,for instance, 180° C. for 10 to 15 minutes. After the pressure isreleased, the composite multi-layered material 8 described in FIGS. 3-6is obtained.

Hereinafter, the preferred embodiments of the present invention will bedescribed in further detail with reference to FIGS. 3-6. In eachembodiment, the composite multi-layered material 8 is manufactured underthe following conditions:

Elementary materials

(1) Finely split pieces--Japanese cedar strand (about 400 mm in length,10 mm in width, 3-4 mm in thickness).

(2) Small pieces--Japanese cedar particle (20 mm in length, 4 mm inwidth, 0.5 mm in thickness).

(3) Adhesive agent--phenol resin.

(4) Condition of thermal pressure molding--180° C. thermal platetemperature, 45 kgf/cm² of pressing and tightening force, 15 minutes ofthermal pressing time.

Furthermore, the shape of the composite multi-layered material 8obtained with each embodiment is approximately 40 cm in length by 40 cmbreadth, 12 mm in thickness, with a specific weight of 0.7. And, thecomposition of the finely split pieces 4 and the small pieces 6 is madeto a 1:1 weight ratio, and various composite multi-layered materials 8were obtained by changing the layering structure.

FIG. 3 is a perspective, partial cutaway view of a first embodiment of acomposite multi-layered material 8 having three layers in accordancewith the present invention. The multi-layered material 8 has athree-layer structure including a structural layer S1, ashock/vibration-absorbing layer P, and a structural layer S1. Theelementary materials used in this embodiment are as above, and theweights of the finely split pieces, small pieces and adhesive agent areas follows. Namely, since the shape of the composite multi-layeredmaterial 8 is 40 cm×40 cm in length by breadth, and 12 mm in thickness,and its specific weight is set to 0.7, its total weight is40×40×1.2×0.7=1,344 g.

Among them, since 10% of the weight of the finely split pieces 4 and thesmall pieces 6 is used for the adhesive agent, its weight is1,344/(10+1)=1,344/11=122.18 g. Accordingly, the weight of the finelysplit pieces and the small pieces is 1344-122.18=1,221.8 g. Since theweight ratio of the finely split pieces and the small pieces is 1:1,each weighs 1,221.8/2=610.9 g.

Next, a manufacturing process will be described. Firstly, one-half ofthe amount of adhesive agent of the above-described weight is spread tothe finely split pieces (weighing 610.9 g) and stirred. The remainingadhesive agent is spread to the small pieces (weighing 610.9 g) andstirred. The finely split pieces and the small pieces which spread theadhesive agent thus are multi-layered within a molding frame 5 as shownin FIG. 2. Next, the finely split pieces 4 (weighing 610.9/2 g) arerespectively arranged lengthwise to form the structural layer S1 as thebottom layer. The small pieces (weighing 610.9 g) are stacked to formthe shock/vibration layer P as the middle layer, and a structural layerS1 is formed again thereon as a top layer so that the lengthwisedirection (e.g., fiber direction) of each of the finely split pieces 4in the top layer is made to be same direction as the lengthwisedirection of each of the finely split pieces 4 of the bottom layer.

Each layer is successively heat-pressed and tightened by the hot press Has shown in FIG. 2(c). Further, during pressing by the hot press, athickness of the stacked body 7 is defined to be 12 mm by using a spacerS which has a height of 12 mm. After the heat-press tightening isfinished, the stacked body 7 is preserved, whereby a compositemulti-layered body 8 as a finished product is obtained.

FIG. 4 is a perspective, partial cutaway view of a second embodiment ofa composite multi-layered material having three layers in accordancewith the present invention. Here, the multi-layered material 8 has twoshock/vibration-absorbing layers P as bottom and top layers, and onestructural layer S1 as a middle layer. The small pieces (weighing610.9/2 g in each layer) are formed in the stackedshock/vibration-absorbing layers P, with each of the finely split pieces(weighing 610.9 g) being arranged in parallel to each other within alayer. Thus, the composite multi-layered material 8 of 40×40 cm inlength by breadth, 12 mm in thickness, and 0.7 in specific weight isobtained.

FIG. 5 is a perspective, partial cutaway view of a third embodiment of acomposite multi-layered material having seven layers in accordance withthe present invention. The composite multi-layered material 8 has aseven layer structure where both the top and bottom layers arestructural layers S1. Moreover, there are a total of four structurallayers which are arranged alternately with threeshock/vibration-absorbing layers. A plurality of finely split pieces(weighing 610.9/4 g in each structural layer S1) are respectivelyarranged in parallel to each other in a lengthwise direction (e.g.,fiber direction) to form each structural layer S1. Eachshock/vibration-absorbing layer P includes stacks of the small pieces 6(weighing 610.9/3 g in each layer P).

The finely split pieces 4 in each structural layer S1 may be arranged sothat the lengthwise direction of each finely split pieces 4 within eachlayer S1 is substantially orthogonal to the finely split pieces 4 ofanother structural layer S1. For example, the pieces 4 of the lowermoststructural layer are orthogonal to the pieces of the second lowermoststructural layer, while the pieces 4 of the uppermost structural layerare orthogonal to the pieces of the second uppermost structural layer.However, the pieces of the second lowermost structural layer areparallel to the pieces of the second uppermost structural layer.

Alternatively, the pieces 4 of the two uppermost structural layers maybe re-oriented by ninety degrees, for example, so that alternatingstructural layers have orthogonal pieces 4. Other combinations willbecome apparent to those skilled in the art. Generally, as discussed infurther detail below, various properties of the material 8 will dependupon the orientation of the finely split pieces 4 of the respectivestructural layers S1. Accordingly, the orientation of the finely splitpieces 4 can be adapted to achieved a desired characteristic of thematerial 8.

With the above arrangements, a plate shaped composite multi-layeredmaterial 8 of 40 cm×40 cm in length by breadth, 12 mm in thickness, and0.7 in specific weight is obtained.

FIG. 6 is a perspective, partial cutaway view of a fourth embodiment ofa composite multi-layered material having seven layers in accordancewith the present invention. Here, the composite multi-layered material 8again has a seven layer structure, but there are fourshock/vibration-absorbing layers P and three structural layers S1.Moreover, the lowermost and uppermost layers areshock/vibration-absorbing layers P. In this embodiment, since there arethree structural layers, the weight of the finely split pieces used foreach layer is 610.9/3 g.

On the other hand, since there are four shock/vibration-absorbing layersP, the weight of the small pieces of each layer P is 610.9/4 g. Firstly,a lowermost shock/vibration-absorbing layer P with the small pieces 6 isformed, and then a plurality of finely split pieces 4 are arranged inparallel to a lengthwise direction to form the lowermost structurallayer S1. Then, a second lowermost shock/vibration-absorbing layer P isformed on the lowermost structural layer. Further, a middle structurallayer S1 of finely split pieces is formed on the second lowermostshock/vibration-absorbing layer so that the lengthwise direction of thefinely split pieces 4 of the middle layer S1 are orthogonal to thelengthwise direction of the finely split pieces 4 of the lowermoststructural layer S1.

Successive shock/vibration-absorbing layers P and structural layers S1are formed as shown. In particular, the pieces 4 of the uppermoststructural layer are arranged to be orthogonal to the pieces 4 of themiddle structural layer. A second uppermost shock/vibration-absorbinglayer P is formed between the middle and uppermost structural layers,and an uppermost shock/vibration-absorbing layer is formed as a toplayer to finally obtain the plate shaped composite multi-layeredmaterial 8 which is 40 cm×40 cm in length by breadth, 12 mm inthickness, and which has a specific weight of 0.7.

In order to verify the capacity of the composite multi-layered material8 in accordance with each of the aforementioned embodiments,measurements of bending strength, peeling off strength, and surfaceroughness were performed.

FIG. 7 is a graph comparing the bending strength of each compositemulti-layered plate shown in FIGS. 3-6. From this test result, it willbe understood that when the layering structure is changed, the bendingstrength will also change. Accordingly, it is possible to tailor thelayering structure to the requirements of different applications. Forthe bending strength in the parallel direction (e.g., the lengthwisedirection of outermost layer of finely split pieces), the embodimentshown in FIG. 3 is strongest. In fact, the bending strength is about 3.2times that of conventional structural plywood. Additionally, theembodiment shown in FIG. 5 has a bending strength which is about 2.5times that of structural plywood, while the embodiments shown in FIG. 4and 6 have similar bending strengths which are approximately 2.2 timesthat of structural plywood.

The bending strength in the orthogonal direction (e.g., the directionwhich orthogonally crosses the lengthwise direction of the outermostlayer of finely split pieces) is similar for the embodiments of FIGS. 4and 5 at about 1.7 times that of structural plywood. The embodiments ofFIGS. 3 and 6 show bending strengths which approximate that ofstructural plywood. It will be understood that, with a three-layerstructure, an isotropic characteristic (e.g., a characteristic differingin capacity by direction) is large, but with a seven layer structure,the isotropic characteristic is small.

FIG. 8 is a graph comparing the bending Young's coefficient of eachcomposite multi-layered plate shown in FIGS. 3-6. Young's coefficient(e.g., modulus), is the ratio of tensile stress to tensile strain in asolid body which undergoes elastic deformation. Furthermore, the tensilestress is the ratio of the deforming force to a cross-sectional area,while the tensile strain is the ratio of a change in length to theoriginal length of the deformed solid.

For the bending Young's coefficient in the horizontal (e.g., parallel)direction, the embodiment of FIG. 3 is highest, with a value which is1.5 times that of structural plywood. The embodiment of FIG. 5 shows animprovement factor of 1.2. The embodiments of FIGS. 2 and 4 have bendingcoefficients which approximate that of structural plywood. In theorthogonally crossing direction, the bending coefficient for theembodiments of FIGS. 4-6 approximate that of structural plywood.

FIG. 9 is a graph comparing the peeling-off strength of each compositemulti-layered plate shown in FIGS. 3-6. The peeling off strength isapproximately constant regardless of the layering structure, and itabout twice that of particle board.

FIG. 10 is a graph comparing a surface roughness of each compositemulti-layered plate shown in FIGS. 3-6. The roughness is defined bycalculating a mean value of thickness which is measured at ten places,and dividing by a standard deviation (e.g., variation coefficient). Theembodiment of FIG. 3 has the highest surface roughness, while theembodiments of FIGS. 4-6 are approximately 60%, 70% and 50%,respectively, of the value of the FIG. 3 embodiment.

From above test results, the following conclusion can be made for thecomposite multi-layered plate material of the present invention:

(a) Young's bending coefficient, bending strength, and peeling offstrength show remarkable improvements over conventional plywood,particle board, and fiber plate;

(b) By changing the layering structure, a strength of a particulardirection is increased, or an isotropic property is decreased. Thus,specific material design capacities can be achieved; and

(c) By using a layer formed by small pieces of wood and the like at theouter surfaces, an improved surface property is possible.

These facts show that the composite multi-layered plate in accordancewith the present invention is a most suitable novel material for use asa structural member for buildings and other structures requiring highquality and capacity structural members.

Note that, although the composite multi-layered material of plate shapein accordance with the above-described embodiments had a specific weightof 0.7, this value means that the mean specific weight calculated fromthe size and weight of the composite multi-layered material is 0.7, andit does not necessarily mean that every part alike has a specific weightof 0.7.

The composite multi-layered material in accordance with the presentinvention forms layers using two kinds of elements which are remarkablydifferent in shape (e.g., finely split pieces of the structural layer S1versus the small pieces of the shock/vibration layer P). Accordingly,the properties of each layer will vary, and the properties of a givenlayer can also vary depending on factors such as the thickness andorientation of the layer. Moreover, the properties of the resultingmulti-layered material will vary according to the characteristics of theconstituent layers.

For example, the shock/vibration-absorbing layer P can more easilyreceive a pressure, and is selectively and strongly compressed. And, thethickness of the various structural layers S1 may vary depending on theposition of the layer within the multi-layer composite. Thus, it may bedifficult to theoretically calculate the specific weight.

Further, according to practical observations of the three-layerstructure, the ratio of thickness of each layer and the weight ratio maybe approximately identical. That is, the weight ratio of each layer,including the adhesive agent, is 336 g:672 g:336 g=1:2:1, and thethickness ratio is 3 mm:6 mm:3 mm=1:2:1. However, for the seven layerstructure, the weight of each layer is relatively small, and,particularly, since the shock/vibration-absorbing layer is stronglycompressed, it was difficult to set their thicknesses even when thecross section is observed. This may be due to the small pieces of theshock/vibration-absorbing layer (which is interposed between thestructural layers) being compressed to a state wherein the small piecesfill gaps between the finely split pieces of the structural layers.

Besides, a goal of the present invention in providing a structure whichalternately arranges the small pieces layers and the finely split pieceslayers is to provide a finished product with a predetermined stiffness.That is, since the finely split pieces are relatively large and stiffelements, a sufficient adhesive force could not be obtained if adjacentlayers both comprised the finely split pieces and the pieces werearranged orthogonally between the layers since the contact area would betoo small. Thus, apart from the case where adjacent layers comprisesfinely split pieces arranged all in one direction, a finished product ofpredetermined stiffness could not be obtained with contiguous structurallayers. In accordance with the present invention, when the small piecesof the shock/vibration layer are interposed between the finely splitpieces of the structural layers while orthogonally crossing the fiberdirections of each other, each layer obtains sufficient adherence to theadjacent layer.

The inventors have further performed a test to measure theanti-shock/vibration capacity of the composite multi-layered materialobtained by structuring the shock/vibration-absorbing layer P as a mixedlayer by adding a vibration-absorbing material to the wood materialsmall pieces 6. In this test, vibration energy is applied to one end ofthe material to be tested, and a loss coefficient of the vibrationenergy at other end is measured. The loss coefficient of the vibrationenergy is an index of attenuation of vibration energy.

Further, in a corresponding embodiment, polyvinyl chloride is used as avibration and energy absorbing material. Details of the structuralelements are as follows.

Elementary materials

(1) Finely split pieces: are molded to a pellet state (particle diameterof about 2 mm); finely split pieces--Japanese cedar strand (400 mm inlength, 10 mm width, 3-4 mm in thickness); small pieces--Japanese cedarparticle (20 mm in length, 4 mm in width, 0.5 mm in thickness); and,vibration-absorbing material--agricultural polyvinyl chloride wastematerial;

(2) Adhesive agent: phenol resin; and

(3) Conditions of thermal pressure molding: thermal platetemperature--180° C.; press-tightening force 45 kgf/cm² ; and, thermalpressing time--15 minutes.

Further, the composite multi-layered plate used for the test had aspecific weight of 0.7, and the shape was 40 cm×40 cm in length bybreath, 12 mm in thickness, and 40 of the wood material small piecesweight was spread and mixed into the shock/vibration-absorbing layer ofthe vibration-absorbing material to form the mixed layer. Additionally,the layering structure, manufacturing method, adhesive agent amount,weight of the finely split pieces and small pieces and the like are thesame as the embodiments described above in connection with FIGS. 3-6.

FIGS. 11 to 14 show graphs which illustrate the measurement losscoefficient of the composite multi-layered material using the mixedvibration/shock absorbing layer.

FIG. 11 is a graph comparing a loss coefficient of the compositemulti-layered plate shown in FIG. 3 with and without a mixedvibration-absorbing layer. The data indicated by the legend "Novibration-absorbing material" in FIGS. 11-14 represents thevibration/shock absorbing layer which uses only the wood material smallpieces. It should be understood that the use of wood material smallpieces alone still provides significant shock absorbing properties. Themixed vibration-absorbing material improves the loss coefficient in thehorizontal (e.g., parallel) direction by a factor of 1.7 compared to theunmixed layer. However, in the orthogonal direction, the losscoefficient is substantially unchanged.

FIG. 12 is a graph comparing a loss coefficient of the compositemulti-layered plate shown in FIG. 4 with and without a mixedvibration-absorbing layer. Here, the mixed vibration-absorbing materialimproves the loss coefficient in the horizontal direction by a factor ofabout 1.8 compared to the unmixed layer, while the improvement in theorthogonal direction is by a factor of about 2.5.

FIG. 13 is a graph comparing a loss coefficient of the compositemulti-layered plate shown in FIG. 5 with and without a mixedvibration-absorbing layer. Here, the mixed vibration-absorbing materialimproves the loss coefficient in the horizontal direction by a factor ofabout 1.4 compared to the unmixed layer. The improvement in theorthogonal direction is by a factor of about 1.5.

FIG. 14 is a graph comparing a loss coefficient of the compositemulti-layered plate shown in FIG. 5 with and without a mixedvibration-absorbing layer. Here, the mixed vibration-absorbing materialimproves the loss coefficient in the horizontal direction by a factor ofabout 1.5 compared to the unmixed layer. The improvement in theorthogonal direction is by a factor of about 2.5.

From above test results, it can be seen that the loss coefficient of thecomposite multi-layered material can be significantly increased byproviding a mixed vibration-absorbing material. Moreover, when thelayering structure is changed, the degree of increase of the losscoefficient is also changed. That is, it will be understood that adesign of the loss coefficient is possible by changing the layeringstructure.

FIGS. 15(a) and (b) are diagrammatic cross sectional views whichillustrate an operational concept of the mixed shock/vibration-absorbinglayer P in accordance with the present invention. In the drawings, S1 isthe structural layer, P is the shock/vibration-absorbing layer, 6 is apellet shaped resin used as the small piece and/or a vibration-absorbingmaterial. The composite multi-layered material 8 is shown in a normal(e.g., non-deformed) state in FIG. 15(a), and in a deformed shape inFIG. 15(b) which is caused by vibration energy due to an applied forceF.

During deformation, an upper side portion of theshock/vibration-absorbing layer P is expanded in the horizontaldirection. The pellet shaped resin used as the small piece and/orvibration-absorbing material is also expanded horizontally as indicatedby the horizontally oblong pellets 6. Moreover, a lower side portion ofthe layer P is contracted along with the pellets. Thus, it is thoughtthat the vibration energy is substantially concentrated to a deformationof the shock/vibration-absorbing layer, and converted to a thermalenergy whereby it is dissipated. Further, it is known that a losscoefficient of a conventional lumbered product is approximately 0.007,and relative to this, it will be understood that a loss coefficient ofthe product in accordance with the present invention has a high value inany of the cases as shown in FIGS. 11 to 14.

FIG. 16 is a graph illustrating a change of Young's coefficient when thetotal weight of the structural layer and shock/vibration-absorbinglayers are equal, and the arrangement of the layers is varied. In thiscase, the composite multilayered material has a specific weight of 0.7as in each of the aforementioned embodiments, and the shape is 400mm×400 mm in length by breadth, and 12 mm in thickness. The ordinate isYoung's bending coefficient, while the abscissa is the distance from theupper surface of the structural layer S1 to the upper surface of thecomposite multi-layered material. Thus, when the abscissa is zero, theupper surface of the composite multi-layered material and the uppersurface of the structural layer are coincident. In other words, thesurface layer is structured by a structural layer (finely split piecelayer) S1 as shown in FIG. 3. Similarly, when the abscissa is 3 mm, theupper surface of the structural layer is located 3 mm from the surfaceof the material, and the surface layer is structured by ashock/vibration-absorbing layer P having a thickness of 3 mm as shown inFIG. 4, for example.

A cross section design of the composite multi-layered materialsatisfying a particular demand capacity is possible by using this graph.For instance, a plate material used for a molding frame of concretefilling-in requires a Young's coefficient of about 70×10⁴ kgf/cm² in thehorizontal (e.g., parallel). direction. Referring to the solid line ofthe graph, it can be seen that an abscissa value of about 1 mmcorresponds to the desired Young's coefficient. Accordingly, the toplayer of the multi-layer composite will be a 1 mm thick P layer. Forsymmetry, the bottom layer will also be a 1 mm thick P layer. Moreover,assuming a plate thickness of 12 mm, for example, a suitable layeringstructure is, beginning from the top layer: P layer (1 mm)+S1 layer (3mm)+P layer (4 mm)+S1 layer (3 mm)+P layer (1 mm). Thus, a compositemulti-layered plate having a capacity required for a concrete moldingframe can be obtained.

FIG. 17 is a graph illustrating a relation of Young's coefficient andthe changes of weight ratio of the structural layer and theshock/vibration-absorbing layer, where the arrangement of the layers isconstant. Various configurations of a composite multi-layered materialhaving three layers are considered. The ordinate of the graph is Young'sbending coefficient. The abscissa is the thickness of the top (e.g.,surface) layer regardless of whether it is a P layer or an S1 layer.

The graph illustrates a change of Young's coefficient when the weightdistribution (and corresponding thickness) of the layers changes for agiven layer arrangement. Two layer arrangements are considered, namelyS1+P+S1, where there are two outer S1 layers and the middle layer is a Player, and P+S1+P, where there are two outer P layers and the middlelayer is an S1 layer. As before, the composite multi-layered materialhas a specific weight of 0.7, and the shape is 400 mm×400 mm in lengthby breadth, and 12 mm in thickness.

For example, with an abscissa value of 1 mm, surface layers (e.g., outerlayers) will have a thickness of 1 mm. Additionally, with an S1+P+S1layer configuration, the thickness and weight of each layer will be: S1(1 mm, weight 112 g)+P (10 mm, weight 1124 g)+S1 (1 mm, weight 112 g).With a P+S1+P layer configuration, the thickness and weight of eachlayer will be: P (1 mm, weight 112 g)+S1 (10 mm, weight 1124 g)+P (1 mm,weight 112 g).

Furthermore, referring to the solid line which includes triangles, itcan be seen that a S1+P+S1 layer configuration with a 1 mm surface layercorresponds to a Young's bending coefficient in the horizontal directionof about 62×10⁴ kgf/cm². Referring to the broken line which includessquares, it can be seen that a S1+P+S1 layer configuration with a 1 mmsurface layer corresponds to a Young's bending coefficient in theorthogonal direction of about 20×10⁴ kgf/cm².

Referring to the broken line which includes circles, it can be seen thata P+S1+P layer configuration with a 1 mm surface layer corresponds to aYoung's bending coefficient in the horizontal direction of about 72×10⁴kgf/cm². Referring to the broken line which includes diamonds, it can beseen that a P+S1+P layer configuration with a 1 mm surface layercorresponds to a Young's bending coefficient in the orthogonal directionof about 18×10⁴ kgf/cm². Thus, a cross section design corresponding to arequired capacity can be determined.

Although the invention has been described in connection with variousspecific embodiments, those skilled in the art will appreciate thatnumerous adaptations and modifications may be made thereto withoutdeparting from the spirit and scope of the invention as set forth in theclaims. For example, while three- and seven layer-composite materialshave been disclosed herein, any number of layer may be used. Moreover,the specific dimensions of the multi-layer material and its constituentelements disclosed have been selected as examples only.

What is claimed is:
 1. A method for manufacturing a compositemulti-layered material, comprising the steps of:(a) splitting a fibrousraw material comprising at least one of wood and bamboo along a fiberdirection to form a first plurality of elongated pieces of said rawmaterial; (b) further splitting said first plurality of elongated piecesof said raw material along the fiber direction to form a secondplurality of elongated pieces of said raw material; (c) drying saidsecond plurality of elongated pieces of said raw material to formelongated dried pieces; (d) arranging said elongated dried piecessubstantially parallel to one another in at least a first structurallayer; (e) applying a first adhesive agent to said elongated driedpieces in said first structural layer to cause said elongated driedpieces to be adhered together in a first adhered structural layer; (f)arranging at least said first adhered structural layer with at least onevibration/shock-absorbing layer in a plurality of layers in analternating manner to form a multi-layered structure; (g) pressing saidmulti-layered structure to a predetermined thickness thereby causingsaid plurality of layers to adhere to one another to provide saidmulti-layered structure as a unitary body; wherein said at least onevibration/shock absorbing layer is obtained by the steps of: (h)providing a plurality of small pieces comprising at let one of wood andbamboo which are smaller than said elongated dried pieces; (i) dryingsaid small pieces to form small dried pieces; (j) distributing saidsmall substantially uniformly in said at least one vibration/shockabsorbing layer; and (k) applying a second adhesive agent to said smalldried pieces to cause said small dried pieces to be adhered together ina first adhered vibration/shock absorbing layer; (l) providing aplurality of resin pellets as load bearing elements; (m) distributingsaid resin pellets in said at least one vibration/shock absorbing layer;and (n) applying said second adhesive agent to said plurality of resinpellets to cause said resin pellets to be adhered together in said firstadhered vibration/shock absorbing layer.
 2. The method of claim 1,comprising the further steps of:(o) providing a third adhesive agentbetween said first adhered structural layer and said at least onevibration/shock-absorbing layer in said multi-layered structure prior tosaid pressing step; wherein said pressing step solidifies said thirdadhesive agent while maintaining said predetermined thickness; and (p)terminating said pressing step after said third adhesive agent of saidmulti-layered structure has solidified to obtain said multi-layeredmaterial.
 3. The method of claim 2, comprising the further steps of:(g)heating said multi-layered structure to a temperature of approximately180° C. substantially concurrently with said pressing step to improve anadhering effect of said third adhesive agent.
 4. The method of claim 1,wherein:a total weight of the structural layer(s) is approximately equalto a total weight of the vibration/shock absorbing layer(s).
 5. Themethod of claim 1, wherein:a weight of said first adhesive agent isapproximately ten percent of a weight of said second plurality ofelongated pieces.
 6. The method of claim 1, wherein:said secondplurality of elongated pieces have a length corresponding to a length ofsaid first structural layer.
 7. The method of claim 1, wherein:saidsecond plurality of elongated pieces have a cross-sectional area ofapproximately 10 mm×4 mm.
 8. The method of claim 1, comprising thefurther step of:arranging said elongated dried pieces in said structurallayer such that said structural layer has a height corresponding to aheight of a plurality of said elongated dried pieces thereof.
 9. Themethod of claim 1, wherein:said resin pellets comprise a denaturedpetroleum resin including at least one of polyvinyl chloride,polyurethane, polyvinyl acetate, acrylic resin, natural gum,butadiene-styrene rubber, nitrile rubber, and chloroprene-copolymer, ora mixture thereof.
 10. The method of claim 1, wherein at least first andsecond vibration/shock absorbing layers are provided.
 11. The method ofclaim 10, comprising the further step of:arranging said first and secondvibration/shock absorbing layers as outermost layers of saidmulti-layered structure.
 12. The method of claim 1, comprising thefurther step of:distributing said small dried pieces with differentorientations in said at least one vibration/shock absorbing layer. 13.The method of claim 1, wherein:small dried pieces have a cross-sectionalarea of approximately 4 mm×0.5 mm.
 14. The method of claim 1, comprisingthe further step of:distributing said small dried pieces in said atleast one vibration/shock absorbing layer such that said at least onevibration/shock absorbing layer has a height corresponding to a heightof a plurality of said small dried pieces.
 15. The method of claim 1,comprising the further steps of:arranging said elongated dried piecessubstantially parallel to one another in a second structural layer;applying a third adhesive agent to said elongated dried pieces in saidsecond structural layer to cause said elongated dried pieces to beadhered together in a second adhered structural layer; and arrangingsaid second adhered structural layer with said at least onevibration/shock-absorbing layer in said plurality of layers to form saidmulti-layered structure.
 16. The method of claim 15, comprising thefurther step of:arranging said first and second adhered structurallayers as outermost layers of said multi-layered structure.
 17. Themethod of claim 15, comprising the further step of:arranging said firstand second adhered structural layers in said multi-layered structuresuch that the elongated dried pieces in the first adhered structurallayer are substantially orthogonal to the elongated dried pieces in thesecond adhered structural layer.